What does the Legendre symbol (D/p) mean in algebraic number theory?

[JasonRox]

http://www.math.uiuc.edu/Algebraic-Number-Theory/0052/

I am given something of the following.

... there is an odd prime p with $$( \frac{D}{p} )$$.

What exactly is that? No, it's not D = p. It's on page 5 if you want to look.

 

[g_edgar]

Legendre Symbol

 

[JasonRox]

Thank you.

I remember writing it without a line... Jeez. I'm going crazy right now.